Electric arc conversion apparatus



May 1948- s. BECKER ETAL 2,441,056

ELECTRIC ARC CONVERSION APPARATUS Filed May 4, 1944 [nvenfor's:

Sam B. Becker Paul E Haw/61y $9 ildvibzdwu Patented May 4,1943

'iJNITED stares ears-NT orri ce Sam B. Becker and Paul F. Hawiey,Chicago, 11]., assignors to Standard Oil Company, Chicago, 1 51., acorporation of Indiana Application May 4, 1944, Serial No. 534,074

(Cl. ace-see 3 Glaims. 1

This invention relates to apparatus for the chemical conversion ofmaterials. More particularly, it is concerned with'apparatus for thetransformation of vaporous or gaseous materials in an electric arc.

The electric arc has long been recognized as a means for the chemicaltransformation of materials. Thus, it has been used for the conversionof atmospheric nitrogen to nitrogen oxides and for the conversion ofnormally liquid and normally gaseous hydrocarbons, e. g. the conversionof methane, ethane, propane, butane or feed stocks containing these.hydrocarbons, e. g. natural gas, to, produce acetylene, ethylene, pro-.pylene, etc., the polymerization of olefinic hydrocarbons, and thecracking of normally liquid hydrocarbons in the vapor phase.

However, electric arc-converters and conversion processes .have, in.commercial practice, failed to achieve an important place primarilybecause of two outstanding problems. These problems are: how to-achievethe substantially complete exposure of the. feedrstream to the electricarc without substantial by-passing, and how to control the temperatureof the. electrodes between which the arc is drawn.

It is an object ofv this invention to provide a novel electrical arcconverter. Another object is to. provide a novel conversion apparatusadapted to produce an annular electrical arc. Still another. object. isto provide means to control the electrode temperature in an electric arcconverter while maintaining a continuous annular arc path. Afurtherobject of this invention is to provide improved processes for vaporphase conversion of materials in an electrical arc. Additional objectsof this invention will become apparent as the description thereofproceeds.

Reference is madetothe accompanying drawings which form a part ofthisspecification and which are. to be read in conjunction therewith.

These drawings illustrate two preferred embodiments of .the inventiombutit is to be understood that these illustrations are not limitations uponthe invention, which is best defined by the appended claims. In thesedrawings the same reference numeral in difierent figures represents thesame or an equivalent part.

Figure 1 represents in diagrammatic form a side view oran arc converterin accordance with our invention, with certain parts shown broken awayfor clarity in representation. v

Figure2 is a diagrammatic view along the line 1-2 of.-Figure1. 5

Figure 3 represents an alternative form of arc 2 converter, largely indiagrammatic cross section.

Figure 4 represents a cross section of'tlie arc converter shown inFigure 3, along the line 4' '4 Essentially the invention comprises achamber containing at least two rotatably mounted cylindricalelectrodes, one of the electrodes being insulated electrical-1y from atleast one" other of the electrodes, the electrodes being. so designedand constructed that when positioned adjacent each other in the chamberthey define at least one substantially circular or annular arc zone inwhich there "is a substantially uniform arc gap. These electrodes .arerotated relative to each other, either by external prime movers; .or byimpellers built into the electrodes, or'by both such means. Feed stockis admitted in the chamber through paths bymeans of which at least amajor part of the feed stock passes'in' the vapor phase directly throughthe annular arc zone across which an electric arc issubstantiallycontinuously' maintained, so that most of the feed stock"is subjected to the. dischargein the are as it passes therethrough.Normally the impellers'assist in directing the'flow'of this feedstock.The chamber is, of course, providedwith means iorremov ing conversionproducts therefrom.

We are acquaintedwith the factthatprior arc conversion processes haveemployed rotating electrodes, for example in United States Patent1,887,658 issued" to Howard S. Nutting et al However, prior arcco'nverters'have been extremely ineflicient, in'that the arc'has beenstruckibetween relativelysmallarcing surfaces so thatthe major part ofthe feed stock by-pas'ses the are which constitutes the true conversionzone. In general such are converters have'been either of the type inwhich there are two oppositelyrotatin'g cylindrical electrodes'mountedend on, or" there have been provided a plurality of projectingelectrodes from a single rotor, opposite whichare located'a fewstationaryprojecting electrodes; With this latter type of constructionone fundamental difiiculty-whi'ch'isexperienced in most are conversionmethods is found; namely, that the elec= trode' surfaces, particularlythe stationary surfaces, become heated by the action of the arc tosuchad'egree that rapid disintegration or erosion of theelectrodefollows; Moreover localizedhigh temperaturesresult in" excessiveuncontrollable decomposition of'the feed stocks, particularlydf theycontain hydrocarbons, and decomposition products are depositedupon thestationary ele'c trode surfaces with resultant' susceptibility topolarization and'extrem'e instability of the are: On the other hand, ii.rotating cylindrical elem 3 trodes are used as taught by the prior art,the arc is struck only in an extremely narrow zone which occupies notmore than a few percent of the total periphery of the electrodes, thusresulting in low capacity apparatus.

On the other hand, essentially the rotating electrodes used in ourconverter define a toroidal arc path around the complete circumferenceof which the arc is substantially continuously maintained, and theoncoming gas is forced substantially completely through this arc,without the substantial by-passing encountered in the prior art. Theelectrodes can be maintained relatively cool due to the fact that theycan be rotated in the gas stream itself.

Referring now more particularly to Figure 1,f

two nozzles H connected through valves I2 to a line l3 containing thefeed stock to be converted, pass through the outer wall of the chamberI4. Within this chamber are two electrodes l5 and i6 which, as shown inFigures 1 and 2, are in the ordinary form of turbine rotors, one mountedwithin theother. These electrodes are formed with substantiallyimpervious parallel side walls within which are mounted a plurality ofimpellers or vanes l1 and I 8. The outer electrode I5 is mounted bymeans of a spider IS on a shaft 2:! which is journaled in a bearing 2|mounted in the walls of the chamber M.

The inner electrode 18 is symmetrically mounted on a second shaft 22coaxial with shaft 20. Shaft 22' is made of insulating material such asany of the present well known high strength insulating plastics. Thisshaft 22 is likewise ro tatably mounted in a bearing 23 borne on thehousing of chamber l4. Suitable conventional gas seals are employed onthe chamber l4 outside of the bearings 2| and 23 to prevent escape of asubstantial amount of gas along the mounting of the shafts. A conductor(not shown) electrically connects electrode l6 through the insulatedshaft 22 to a slip ring 24 mounted on the shaft external to the chamberM. An alternator 25 or other suitable source of arc voltage is connectedto the case I4 (which in turn is grounded) and the slip ring 24, bymeans of which arc voltage is applied between the rotatable electrodesl5 and [6.

The gas passing in through nozzles ll impinges upon the impellers H ofthe outer electrode I5, in part'causing it to rotate in the directionshown by the arrow, and causing substantially all of this gas to beforced into the annular space or zone 26 between the inner and outerelectrodes. It is to be noted that there is a substantially uniformdistance between these electrodes l1 and I8 in this annular zone 26.This zone therefore forms the annular arc zone of the converter. The gaspassing through this zone in part escapes from between the electrodesand in large part passes through and impinges upon the impellers orvanes I8 of the inner electrode l6, thereby assisting it to rotate inthe opposite direction from that of electrode I5. In either case, thegas containing the converted products due to the action of the arcpasses to an exit volute 21 from which it can be removed through avalvedline 28. Since there is a substantially uniform arc gap throughout theannular zone 26 between the electrodes, the voltage due to the source 25causes an arc to form substantially in a ring form throughout the entireannular volume, thus exposing practically all of the inlet vaporous feedstock to the action of the arc. r

Either or both of the coaxial shafts 2|! and 22 may be connected toprime movers which assist in rotating the electrodes in the desireddirection. The combined action of the blast of gas passing through theelectrodes and their rotation in the gas stream keeps the electrodes ata temperature far below that at which there is substantial accumulationof undesirable decomposition products. For example, if a hydrocarbonfeed stock such as natural gas is employed, the combined action of thegas blast and the rotation of the electrodes serves to minimize theaccumulation of solid carbonaceous material in this zone, for example inthe form of carbon trees, with resultant avoidance of short-circuitingof the apparatus which would necessitate frequent shutdowns.

Another important advantage of the equipment just described is that bythe use of the impellers or vanes shown on the electrodes, whichimpellers or vanes l5, l6 and 40, 4| form continuous sinuous passagesthrough the electrodes communicating directly with the annular arc zones26 and 44 respectively, the gas is forced to take a predeterminedsinuous path through and between the electrodes and, since the passagesformed communicate with the annular arc zones at an oblique angle, thegas has a large tangential component of velocity, thus tending tomaintain it in the arc zone for a greater length of time than would betrue if it travelled solely in a radial direction. This tends to reversethe direction of the gas as it passes from one set of impellers to theother and gives a more complete conversion of raw feed stock into thedesired products. This reversal also aids in the scrubbing action,tending to keep the electrode surfaces exposed to the are both cool andclean.

It is also apparent that by the use of this equipment it is possible totreat substantially all of the incoming 'gas through the ring-like orannular arc with a minimum of by-passing and a maximum conversion perpass. However, it is cocasionally advantageous to recirculate at least apart of the material removed from the are converter, as will besubsequently described.

It is desirable to insure that any solid or liquid conversion product beprevented from settling on the portion of the shaft 22 within thechamber I 4. We have shown two ways of avoiding this difiiculty inFigure 2. If desired, a flushing liquid (for example, a liquidhydrocarbon such as kerosene, naphtha, virgin or cracked gas oil, highboiling aromatic hydrocarbons or the like) may be admitted throughvalved line 29 and pumped by pump 30 through one or more spray nozzles3| upon the shaft 22 adjacent to the bearing 23 in a directionapproximately parallel to the shaft 22, by means of which the shaft isbathed with the flushing liquid, and any accumulation of the conversion.products is prevented or substantially minimized. The excess flushingliquid accumulates in the bottom of chamber I 4 and is removed throughline 732', preferably being passed through filter 33 and recirculated bypump 30; Additional flushing liquid is added through line 29 as needed.

On the other hand, both to clean shaft 22 and thus assist in preventingarcing at this point, and to recycle some of the material removed fromthe converter, apart of this removed material can be withdrawn from theexit volute 21 and passed through valved line 34, and impelled by pump35 through nozzle 36 along shaft 22, preferably in a directionapproximately parallel therewith. The

Zara-am gas. blast due to. this. nozzle (oi which-there be. several),tends. to. avoid retention. of solid or. liquid particles on. this.shaft, thus-maintainin its} insulating properties. The, material forced:in through the nozzle 36- eventually passes through the arc region andisthen.- againremoved through the volute 21. It should be understood thatwe contemplate the simultaneous employment; of liquid flushing andagasblast .tokeep shaft 22 clean.v

Theflushing material, particular-1 pm the case oi hydrocarbon feedstocks, is preferablyone having, a relatively low vapor press.ure,.relatively high. resistance to thermal decomposition, high electricalresistivity, and high solvent or dis:- persing power for carbonaceousresiduessuchas are produced. by excessive thermal decomposition oi.hydrocarbons. We contemplate that the flushing fluid entering through:valved line- 29 may have: incorporated therein or besubstan.- tially.composed of a detergent or dispersinggmaterial capable of dissolving ordispersingifinelydivided metal and carbonaceous particles; For example,alkyl. aryl sulfonates,v such as dodecyl benzene sodium sulfonate,dialkyl esters ofsodium sulfosuccinate, detergentcompositions of thekind described in U..S. Patent-2,316,083 issued to C. M. Loane et al.,or other known dispersing; or detergent materials may be employed forthis purpose.

The operating. conditions, including peripheral velocitiesv or relativevelocities of the rotatable electrodes I 5 and it, the velocity ofvtheentering material throughnozzles H,,the arc. temperature, thepressure within the vessel, and the rate of withdrawal of conversionproducts, necessarily influencethe nature and extent of the reactionsbeingeffected in thearc converter. The operating conditions are notsusceptible of precise definition except with respect to. a. particularfeed stock when a particular product distribution is desired.

It is, of course, to be recognized that more than two nozzles H can beadvantageously employed or that, under some conditions only one nozzlemaybe necessary, and that the. number and. position of'the vanes orimpellers 1.1. and IB-may depend largely upon the conversion:operationundertaken. v v

In Figure 3 another d'esirableiform t arc. converter is shown. In thiscase two cylindrical electrodes in and 4'! 'are, coaxiallyand rotatablymounted adjacent each other inside achamber 42;. As. can be seen fromthe part of electrode 41 shown broken away, these electrodes, preferablycontain a plurality of" vanes or impellers and are so constructed thatthe outer adjacent portions of the electrodes form a considerablynarrower gap than thatiormedbythe inner portions of the electrodes.This. substantiallycircular gap- A l defines an annular. arc zone, Thecylindrical electrodes 40 and ii are mounted on shafts 45 and 46respectively, which are mounted on bearings 41 and 48, which in turn aremounted on insulating bushings 49 and 50, suitably insulating theseshafts from the chamber 42. These shafts 45 and 46 may be connected byinsulated couplings (not shown) to prime movers which tend to rotate thetwo electrodes in opposite directions. The impellers mounted within therotating electrodes 40 and M assist in this rotation as will besubsequently discussed. An alternator or other suitable source of arcvoltage is connected through brushes 52 and 53 with the shafts 45 and 46.by means of which the: arc voltage: iaappIied across the gap; .4discussed above, thus causing a ring on annular arcstoiformiini.thisezonea The" feed; stock is: admitted. to: the. chamberthrouglrvalved; line: 55-. It is. forced: to; pass into the'space; 55adjacent the: arc, zone: by at baiilez 56 which causesv the feed stock.to how in the: direction showniby the arrows, adiacent to the bearing lland approx-imately,- paralleL to: the; shaft 45. feed. stock; entering;this. central space; 55 close; to the. shaftfii passes throughtheimpellers mounted within the electrode 40=-andsis-iorced thereby intothe. annular zone: 4.4 through which it passes outwardly with:boll-1132:. radial.v and a tangential component, thus maintaining. it.for aconsiderable; lengthzof: pathein the-amend serving;simultaneous1y5-'-to= cool the: arc: surfaces: of electrodeAU- and.maintain theme/ta desirableerelatively low temp eratura. The. materialwhich: has passed.- outwardly.- from-this. zone, including; theconversion ,productapassesiin theidirectionshown by the. arrow, apart.of it passing throughwthe openingin baflle. 51,. and. apart passingvback through electrode 4-4- dueto. the impellers, con,- tained therein,itthus beings. immediately recydedvthroughlthezannular arc zone: Thematerial which passes through: the opening; in: bafile 51 is. removedthrough-liner 58: and is: withdrawn from the: converter throughdine- 5aand valved line 59;

It it is. desired :to: recycle apart of the materialleaving,- the. arcconverter, it ismerely necessary to.- open-the: valve in linev 60.andeimpel this material by? means oi;- pump: B-tthroughvalved line.- 62'back. through-line: 54 into; the converter.

It is seen that wim this arrangement-0f equin ment, substantially allotthervaporouafeed, stock entering; line: 54- is. forced:throughrthe'annular arc: zone 44, .lIhllSi giving; a. highly efficienttarc conversion, while-the blast of theegas; passing through the: two;electrodes. serves: to keep'these electrodes coolv andi clean.v

Converted materials issuing,- from; our are converterbe subjected; to.-one-or more of a variety of. operations resulting ina'thei segregaetion. or purification or conversion productafrom unconverted materialsuitable for: recycle to; the same on a different arcconverter-Thuathe-converted material: from, ourerc: converter may, be subjected:to refrigeration, compression; absorption; filtration,fractional,distillation; orsimilar operations for. vthesegregation ofcarbonaceous-or tarry: materials;,,normally liquid materials: andnormallygaseous materials. The: electric arc comrertersof our inventiomcan: be useda singly, either on a: onceethrough; or recycle: basis, or.a plurality: of converters: may-be; usedv series or parallel with or:without; product separation: be.- tween: 5118\V8i1i0l15 conversion.stages;

The directionand extent: of? ther conversion within: the annular: arccan be influenced by the passage oi: catalytic materials withthevaporous feed through the conversion zone. A wide variety of catalystsis available for use, depending upon the specific conversion sought tobe effected. Thus, hydrocarbon conversion may be influenced by thepresence of such catalysts as the active halides, e. g. the halides ofhydrogen, boron, zinc, tin, iron and the like. In addition the arcconversion can be influenced by the material of which the electrodes arecomposed, although customarily the electrodes are maintained at asufiiciently low temperature so that there is no substantialvaporization of this material. Suitable electrode materialsinclude'iro'n, aluminum, cobalt alloys,

carbon, etc.

The are converters of our invention will be found particularlyadvantageous for the conversion of light hydrocarbon gases, particularlywhen accompanied by a reactive gas such as oxygen, halogens or halogenacids, to produce partial oxidation, halogenation, or the like.Specificallythe apparatus of our invention is Well adapted for theproduction of unsaturated hydro ed in said chamber, an inner ringelectrode concentrically mounted within said outer ring electrodewhereby an annular arc zone with a continuous substantially uniform arcgap is formed be tween said electrodes, said electrodes being rotatable,said ring electrodes including a plurality of vanes forming radialpassages extending through each of said electrodes and communicatingwith said annular arc zone, means for introducing a feed stock into saidchamber adapted to direct at least a major portion of said feed stockthrough the passages of said outer electrode at a high velocity, saidpassages in said outer electrodes being so shaped as to direct the feedstock introduced therein through the annular arc zone and through thepassages of said inner electrode and said passages of said rotatableelectrodes being so shaped so as to produce-rotation of said electrodesupon passage of the feed stock therethrough, means for removingconversion prod ucts from said chamber, means for electricallyinsulating one of said electrodes from the other, and means for applyingelectric arc voltage be-- tween said electrodes for producing asubstantially continuous annular arc in said are zone.

2. An electric arc conversion apparatus comprising a chamber, a firstring electrode mounted in said chamber, a second ring electrode mountedwithin said chamber whereby an annular arc zone with a continuoussubstantially uniform arc gap is formed between said electrodes, saidelectrodes being rotatable, said ring electrodes including a pluralityof vanes forming passages extending through each of said electrodes andcommunicating with said annular arc zone, means for introducing a feedstock into said chamber adapted to direct at least a major portion ofsaid feed stock through the passages of said first electrode at a highvelocity, said passages in said first electrode being so shaped as todirect the feed stock introduced therein through the annular arc zoneand through the passages of said second electrode, and said passages ofsaid rotatable electrodes being so shaped as to produce rotation of saidelectrode upon passage of the feed stock therethroush, means forremoving conversion products from said chamber, means for electricallyinsulating one of said electrodes from the other, and means for applyingelectric arc voltages between said electrodes for producing asubstantially continuous annular are in said are zone.

3. An electric arc conversion apparatus comprising a chamber, a firstring electrode rotatably mounted in said chamber on a shaft, a secondring electrode mounted within said chamber rotatably carried by a secondshaft coaxially arranged with the first named shaft whereby an annulararc zone with a continuous substantially uniform arc gap is formedbetween said electrodes, said ring electrodes including a plurality ofvanes forming passages extending through each of said electrodes andcommuni eating with said annular arc zone, means for introducing a feedstock into said chamber, means adapted to direct at least a majorportion of said feed stock through the passages of said first ringelectrode at a high velocity, said passages in said first ring electrodebeing so shaped as to direct the feed stock introduced therein throughthe annular arc zone and through the passages of said second ringelectrode, said passages being so shaped as to produce rotation of saidsecond electrode upon passage of thefeed stock therethrough, means forremoving conversion products from said chamber, means for electricallyinsulating one of said electrodes from the other, and means for applyingelectric arc voltage between said electrodes for producing asubstantially continuous annular arc in said arc zone.

SAM B. BECKER. PAUL F. HAWLEY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 707,797 Otto Aug. 26, 1902829,874 Lovejoy Aug. 28, 1906 1,051,131 Lee Jan. 21, 1913 1,316,445Island Sept. 16, 1919 1,317,705 Island Oct. 7, 1919 1,336,939 BarfoedApr. 13, 1920 1,887,658 Nutting et a1 Nov. 15, 1932 1,931,800 Jakosky etal Oct. 24, 1933 1,948,240 Redd Feb. 20, 1934 2,320,391 Wakefield June1, 1943 FOREIGN PATENTS Number Country Date 211,125 Great Britain June2, 1925 331,315 France July 24, 1903 356,413 Germany July 19, 1922

